Query for Locations within a Circle on a Sphere

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About this Task

Before You Begin
Procedure
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You can query for location data within a circle on the surface of a sphere. Use these queries to return data within a spherical cap.

To query for location data within a circle on a sphere, use $geoWithin with the $centerSphere operator. In the $centerSphere operator, specify the coordinates and radius of the circle to query within:

db.<collection>.find( {
   <location field> : {
      $geoWithin : {
         $centerSphere: [
            [ <longitude>, <latitude> ],
            <radius>
         ]
       }
    }
 } )

About this Task

When you specify longitude and latitude coordinates, list the longitude first, and then latitude.
- Valid longitude values are between -180 and 180, both inclusive.
- Valid latitude values are between -90 and 90, both inclusive.
In the $centerSphere operator, specify the circle's radius in radians. To convert other units to and from radians, see Convert Distance to Radians for Spherical Operators.
- This example calculates distance in kilometers. To convert kilometers to radians, divide the kilometer value by 6378.1.
$geoWithin does not require a geospatial index. However, a geospatial index improves query performance. Only the 2dsphere geospatial index supports $geoWithin. For more information see Create a 2dsphere Index.

Before You Begin

Create a places collection that contains these documents:

db.places.insertMany( [
   {
      loc: { type: "Point", coordinates: [ -73.97, 40.77 ] },
      name: "Central Park",
      category : "Park"
   },
   {
      loc: { type: "Point", coordinates: [ -73.88, 40.78 ] },
      name: "La Guardia Airport",
      category: "Airport"
   },
   {
      loc: { type: "Point", coordinates: [ -1.83, 51.18 ] },
      name: "Stonehenge",
      category : "Monument"
   }
] )

Procedure

To query the collection, use $geoWithin with the $centerSphere operator:

db.places.find( {
   loc: {
      $geoWithin: {
         $centerSphere: [
            [ -1.76, 51.16 ],
            10 / 6378.1
         ]
      }
   }
} )

The query returns documents where the loc field is within a 10 kilometer radius of a point at longitude -1.76, latitude 51.16.

Output:

[
   {
     _id: ObjectId("63fd205e4a08b5e248c03e32"),
     loc: { type: 'Point', coordinates: [ -1.83, 51.18 ] },
     name: 'Stonehenge',
     category: 'Monument'
   }
]

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